What was found
WHEN ATTEMPTING TO CALL DISPATCH OVER SATCOM NEITHER SAT 1 OR SAT 2 WORKED. ALL INDICATION WERE NORMAL BUT THERE WAS NO VOICE OR CARRIER. GROUNDED-YES. VERIFIED PREVIOUS TROUBLE SHOOTING, ABLE TO PLACE CALLS TO DISPATCH AND COMMUNICATE, DISPATCH UNABLE TO CALL A/C DUE TO TECHNICAL ISSUES ON THEIR END. USED ALTERNATE METHOD VIA IRIDIUM SATCOM TELEPHONE NUMBER, INCOMING CALL OPERATIONS NORMAL. OUTGOING AND INCOMING CALLS OPERATIONS NORMAL, REF B737-900 AMM 23-15-00.